LoRa Martin Heusse LIG / Drakkar Lora in the ISM bands channel - - PowerPoint PPT Presentation

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LoRa Martin Heusse LIG / Drakkar Lora in the ISM bands channel - - PowerPoint PPT Presentation

Jan 19, 2024 241 likes •456 views

LoRa Martin Heusse LIG / Drakkar Lora in the ISM bands channel spacing : 200kHz 433MHz Band Max Tx power 10dBm EU 863-870MHz Band Max Tx power : 20dBm, by default 14dBm Rx channels for the gateways 12 Modulation

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SLIDE 1

LoRa

Martin Heusse LIG / Drakkar

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SLIDE 2

LoRa — page 2 — transp. 2

Lora in the ISM bands channel spacing : 200kHz

  • 433MHz Band

✓ Max Tx power 10dBm

  • EU 863-870MHz Band

✓ Max Tx power : 20dBm, by default 14dBm ✓ Rx channels for the gateways

LoRa™ Alliance

ht to c

12

Modulation Bandwidth [kHz] Channel Frequency [MHz] FSK Bitrate or LoRa DR / Bitrate Nb Channels Duty cycle LoRa 125 868.10 868.30 868.50 DR0 to DR5 / 0.3-5 kbps 3 <1% Table 12: EU863-870 default channels

13 Toff = TimeOnAir DutyCycle − TimeOnAir –

✓ Duty cycle is computed per sub band ✓ Each gateway may listen to 16 canaux in parallel. Specified to the devices when they associate

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SLIDE 3

LoRa — page 3 — transp. 3

Lora in the ISM bands channel spacing : 200kHz (cont.)

LoRa™ Alliance

  • –

in the EU863-870 band: 18

DataRate Configuration Indicative physical bit rate [bit/s] TXPower Configuration LoRa: SF12 / 125 kHz 250 20 dBm (if supported) 1 LoRa: SF11 / 125 kHz 440 1 14 dBm 2 LoRa: SF10 / 125 kHz 980 2 11 dBm 3 LoRa: SF9 / 125 kHz 1760 3 8 dBm 4 LoRa: SF8 / 125 kHz 3125 4 5 dBm 5 LoRa: SF7 / 125 kHz 5470 5 2 dBm 6 LoRa: SF7 / 250 kHz 11000 6..15 RFU 7 FSK: 50 kbps 50000 8..15 RFU

Table 14: Data rate and TX power table

19

  • Real world range : a few km NLOS, ≈ 20 km with

LOS

  • Payload max size : from 59 to 230 B

( for datarate 4 and higher)

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SLIDE 4

LoRa — page 4 — transp. 4

ISM 868MHz band http://www.arcep.fr/uploads/tx_gsavis/14-1263.pdf

http://www.anfr.fr/fileadmin/mediatheque/documents/tnrbf/TNRBF_

Ed2013_Mod8_-_Version_du_19_février_2016.pdf

EIRP: 14dBm Freq. Duty cycle

  • ther uses

863-865 MHz 0,1 % Cordless microphones 865-868 MHz 1% RFID – ?? 868-868,6 MHz 1% (802.15.4 Sub-GHz) 868.6-868,7 MHz — Alarms 868,7-869,2 MHz 0,1% 869,2-869,7 MHz — Alarms 869,7-870 MHz 1% air force

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SLIDE 5

LoRa — page 5 — transp. 5

ERC Recommendation 70-03

http://www.erodocdb.dk/docs/doc98/official/pdf/rec7003e.pdf

Sub band

  • Freq. (MHz)

Power Duty cycle BW (MHz) h1.3 863-870 14 dBm 0.1% 7 h1.4 868-868.6 14 dBm 1% 0.6 h1.5 868.7-869.2 14 dBm 0.1% 0.5 h1.6 869.4-869.65 27 dBm 10% 0.25 h1.7 869.7-870 7 dBm 100% 0.3 h1.7 869.7-870 14 dBm 1 % 0.3

Duty cycles are computed per sub-band : a device may consume 1% in h1.4, 10% in h1.6, 1% in h1.7, during the same hour for instance h1.4 encompasses the 3 defaults LoRa channels, h1.6 is used by the GW to respond to the devices (cf. RX2)

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SLIDE 6

LoRa — page 6 — transp. 6

Transmissions

  • Classe A (All devices)

✓ Exchange always initiated by the device Aloha access ✓ 2 rx windows follow the transmission at +1 s (same channel as TX) and +2 s (channel and SF fixed in advance)

LoRa™ Alliance

the rig

‘s

By default : RX2 at 869.525 MHz (center of h1.6), DR0 (SF12, 125 kHz) ✓ Each frame carries the Confirmed bit: (expecting and ACK) or unconfirmed

  • Classe B : Beacons Device listen periodically to beacons. Regular downlink

slots are defined relative to the beacon

  • classe C : Continuous reception
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SLIDE 7

LoRa — page 7 — transp. 7

LoRaWAN

GW GW Network Server App Server App Server App Server LoRa / JSON / UDP SSL/TCP/IP Concentrator Concentrator

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SLIDE 8

LoRa — page 8 — transp. 8

LoRaWAN (cont.)

LoRa™ Alliance Radio PHY layer: 6

Preamble PHDR PHDR_CRC PHYPayload CRC*

Figure 5: Radio PHY structure (CRC* is only available on uplink messages)

7 PHYPayload: 8

MHDR MACPayload MIC

Figure 6: PHY payload structure

9 MACPayload: 10

FHDR FPort FRMPayload

Figure 7: MAC payload structure

11 FHDR: 12

DevAddr FCtrl FCnt FOpts

Figure 8: Frame header structure

13

4B 1B … 4B 1B 2B 0…15B 0 or 1B …

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SLIDE 9

LoRa — page 9 — transp. 9

LoRaWAN (cont.)

  • The frames only carry a single address, the device

source/destination

  • Application demultiplexing : “FPort” (0: pure MAC command)
  • Piggybacking of MAC commands (power, data rate, channels,

device state, rx delay1 … ) in the will typically get several copies

  • f the same frame (they have a seq. number)

The net. server selects the best GW for a reply (if applicable)

  • In the core networks, the frames are forwarded with quite a bit
  • f ancillary data (power, timestamp…)

1RX2 is always 1 s behind RX1

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SLIDE 10

LoRa — page 10 — transp. 10

Activation

  • ABP — Activation By Personalization
  • OTAA — Over-The-Air Activation

✓ DevAddr allocation: the DevAddr is composed of 7 bits of Network ID and then a device-specific addr. (The DevAddr is assigned by the guest network. The real / immutable device identifiers are its NetEUI and AppEUI, which are stored in the device) ✓ Computation of the session keys: AppSKey, NetSKey, from the AppKey (128 bits) stored in the device

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SLIDE 11

LoRa — page 11 — transp. 11

What is a chirp ? CSS : Chirp Spread Spectrum

  • A linear frequency sweep/ramp − BW

2 < f < BW 2

−4 −2 2 4 −1.0 −0.5 0.0 0.5 1.0 t tx(x)

  • Used by radars, bats, dolphins…
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SLIDE 12

LoRa — page 12 — transp. 12

Coding information on a chirp

  • It is the start freq. offset that codes the information (line 514)
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LoRa — page 13 — transp. 13

Reception

  • Multiplication of rx signal with a complex conjugate chirp (down

chirp)

e2πjt[f0+(at+b) mod BW] × e−2πjt[f0+(at) mod BW]

= e2πjt[b mod BW]

N.B. : a = BW2

2SF → sweep BW in time 2SF BW

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LoRa — page 14 — transp. 14

Reception (cont.)

  • if both chirps are in sync, we get a constant, otherwise
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LoRa — page 15 — transp. 15

FFT-based reception

  • FFT after sampling at rate BW
  • The symbol duration is N/BW → N samples
  • By frequency aliasing, a single frequency appears in the

FFT !

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SLIDE 16

LoRa — page 16 — transp. 16

Spread spectrum

  • Spreading factors from 7 to 12 ⇔ N goes from 27 to 212,

7 to 12 bits per symbol

  • The bigger the SF the longer the chirp — 33 ms @ SF12.

For LoRa, the preamble is also proportional to the SF

✞ ✝ ☎ ✆

The actual SF dynamics are ≈ 20 Rb = SF × BW

2SF

  • Error correcting codes R = 4

5

  • The actual max. SF is ≈ 340 (212/12), so a transmission may

survive a collision with a node closer by a ratio of ≈ √ 340

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SLIDE 17

LoRa — page 17 — transp. 17

Frame sizes

  • Depends on SF : 51B payload at SF12, 242 at SF8 and SF7…
  • 51B @ SF12 → 1,3 s of continuous transmission!
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SLIDE 18

LoRa — page 18 — transp. 18

Initial Synchronisation

t f

f-BW/2 f+BW/2 N/BW

Preamble ∂f, ∂t

Receiver :

Data 2 inverted chirps

  • The device may quickly assess if there is a transmission → short

rx1 and rx2 windows

  • The inverted chips in the preamble allow to find the two

unknown variable the transmitter frequency and the relative time reference

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LoRa — page 19 — transp. 19

Localization

  • The observed δt at several GW allow to compute relative time
  • f arrival
  • Trilateration
  • Time ref. from GPS at the GWs
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LoRa — page 20 — transp. 20

A few remarks

  • A receiver can receive at several SF simultaneously (≈ 30 dB)2.
  • It needs as many reception circuits as there are SFs

7 channels (6 CSS + 1 FSK) on all LoRa GWs

  • Localization is a by product of PHY initial sync.
  • Cell breathing

✓ Having more GWs allows :

▶ Lower the SF for closer devices ▶ lower the power

  • 2C. Goursaud & J.M. Gorce : “Dedicated networks for IoT : PHY / MAC state of

the art and challenges”